A STUDY into the origins of man has cast doubt on the idea that Homo sapiens evolved from a single population of ancestors who lived in Africa.

The findings challenge the idea that there was a single cradle of humankind somewhere in sub-Saharan Africa about 100,000 years ago, where the first recognisably contemporary people lived in isolation from other hominid species.

A study of the variation within a single human gene has been used to reconstruct evolutionary events dating back several million years. A genetic analysis of 16 Africans and 19 non-Africans revealed mutations in the gene that could have come about only after the division of the ancient population when our ancestors were starting to trek out of Africa.

Present-day Africans have a lot of variation - mutations - in the gene compared with Europeans and Asians, indicating that the forces of evolutionary change had worked on at least two separate ancestral populations.

"We found a gene in humans that has a very interesting history," said Dr Jody Hey, a visiting research fellow in genetics at the University of Edinburgh, co-author of the work published in the Proceedings of the National Academy of Sciences. "It provides evidence of a split in the ancestral human population at about 200,000 years ago, separating Africans and non-Africans. What's unique about our study is that it yields a date when population splitting first started."